1. Field of the Invention
The present invention relates to a vehicular brake system component, such as an accumulator, used in a brake system of a vehicle.
2. Description of the Related Art
A known vehicular brake system component, e.g., an accumulator, comprises a pressure vessel and a diaphragm. The pressure vessel has a gas chamber in which a compressed gas is sealed and a liquid chamber filled with a liquid, such as oil. The diaphragm divides the gas and liquid chambers and has one end capable of extending and contracting in the axial direction of the vessel. The diaphragm of the accumulator of this type requires elasticity to cope with change in volume of the gas, as well as high gas barrier performance (high gas impermeability). Therefore, the diaphragm is expected to be flexible and highly durable.
In the case of the accumulator of which the interior of the pressure vessel is divided into the gas and liquid chambers by the diaphragm, however, the diaphragm sometimes may excessively extend or contract when the gas is sealed into the gas chamber or if the pressure in the liquid chamber falls below a given level during use. If the diaphragm excessively extends or contracts in this manner, it is partially pressed against the inner surface of the pressure vessel. Thus, an undue force may possibly locally act on a seal member provided on an elastic end of the diaphragm, thereby spoiling the sealing performance.
A known accumulator is described in Jpn. Pat. Appln. KOKOKU Publication No. 6-1092. In this accumulator, a partition wall is located in a liquid chamber, and a lid (seal member) is provided on an elastic end of a diaphragm. The partition wall has a circulation port in a position opposite the elastic end of the diaphragm. Oil in an oil chamber flows through the circulation port when the diaphragm extends or contracts with the port communicating with the oil chamber. The lid is formed of a rubberlike elastic body of synthetic resin.
When the diaphragm fully extends or contracts, according to this accumulator, some of oil that is previously stored in the liquid chamber is confined to the liquid chamber side of the diaphragm (between the partition wall and the diaphragm) by the lid. Since the liquid is substantially noncompressive, the diaphragm is prevented from further extending or contracting by the confined backup liquid or oil.
The seal member for confining the backup liquid is always immersed in a liquid that is introduced into the liquid chamber. The accumulator is used in a hydraulic-pressure device that is mounted in a vehicle, for example. Preferably, therefore, the seal member should be able to secure satisfactory sealing performance for a prolonged time, as well as chemical resistance and durability against pressure fluctuation at high temperature.